There Could Be Three Different Types of Tyrannosaurs

There Could Be Three Different Types of Tyrannosaurs

A new analysis of tyrannosaur skeletal remains reveals physical differences between the hipbone, other bones, and dental structures across samples. According to the new study, published two days ago in Evolutionary Biology, this indicates that Tyrannosaur rex specimens should be reclassified and assigned to three separate groups or species.

Tyrannosaur rex is the only known species of the Tyrannosaur dinosaur group or genus to date. Previous research has shown variations in skeletal remains in the hipbone of Tyrannosaurs, with specimens containing one or two fine incisors on either side of the anterior ends of the jaw.

Gregory Paul and colleagues analyzed the bones and dental remains of 37 Tyrannosaur specimens. The authors of the article compared hip bone strength in 24 of the samples. This measure, calculated from length and circumference, gives an idea about the durability of the bone. The scientists also measured the diameter of the base of the tooth, or the area between the gums, to assess whether the species contained one or two fine incisors.

The authors of the paper observed that the hip bone varied across species, with some having stronger hip bones, while others having weaker hip bones. Researchers found that across species, hip bones were twice as strong as weaker ones. This shows that the difference in question is not due to gender. If it was due to gender, there would probably be a much more even split. The authors of the article also stated that this variability in hip bones was not related to the growth of the sample; because the strong hip bones found in some young specimens are two-thirds the size of an adult, and the weak hip bones found in some specimens are also the size of a full adult.

The dentition also varies between species, although the amount of both the hip bone measured and the dental remains were low (12 samples). The hip bone was generally weaker in specimens with one incisor.

28 of the tyrannosaur specimens appeared in separate layers of sediment (stratigraphy) in the upper Mastrichtian Lancian formations (estimated from 67.5 to 66 million years ago) in North America. The authors of the paper compared Tyrannosaurus specimens with other theropod species found in lower sedimentary layers.

Combined with the layer information, the physical variations found in Tyrannosaur samples, the authors concluded, point to three possible groups that could be nominated as two new species, T. imperator and T. regina, as well as T. rex, the only species recognized to date.

The famous Tyronosaur rex, the only known species in the genus Tyrannosaurus so far. Depiction: Fausto García-Menendez/Unsplash Source: 

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